How to Sanitize a Water Tank With Bleach

Here are some potential uses that may apply to your situation:

1. If you have a tank with clear water that you simply want to make sure is safe to drink or use for human contact (hand washing, laundry, etc.), then you can follow the protocol for emergency disinfection of drinking water. In that case, the correct ratio of bleach is 1 teaspoon Clorox^® Disinfecting Bleach per 7 gallons of water (or for a smaller size container, 4 drops per quart). Stir the bleach into the water and let stand 30 minutes. Properly treated water should have a slight chlorine odor—if not, repeat the dosage and let stand an additional 15 minutes.
2. To clean out a water tank, thoroughly flush the tank using a bleach solution made with 1/3 cup Clorox^® Disinfecting Bleach per 3 gallons water (a 500ppm bleach solution). I’m not sure of the size of your tank or how much bleach solution you will need to clean the tank, but here’s one example: to make approximately 9 gallons of bleach solution, then you would start with 9 gallons of water, and then add 1 cup bleach. After flushing the tank with the 500ppm bleach solution for 5 minutes, then rinse with a 10ppm bleach solution (1 teaspoon bleach per 10 gallons of water).

You may also want to get some chlorine test strips to confirm the bleach concentration of the solutions you mix up. These can usually be found at pool supply stores.